Difluoromethane (F-32) can be manufactured by fluorination of dichloromethane or methylene chloride (F-30). For example, the documents FR 2736050 and FR 2748022 describe the fluorination of F-30 to give F-32 in the gas phase in the presence of solid catalysts.
The document U.S. Pat. No. 6,268,540 describes the liquid-phase fluorination of hydrohalomethanes, and notably that of F-30, using pentavalent molybdenum, niobium, titanium or tantalum halide catalysts. The short duration of the reactions illustrated does not make it possible to know the lifetime of these catalysts.
The document U.S. Pat. No. 6,407,296 describes the use of antimony pentafluoride, or of a mixture of antimony pentafluoride and antimony trifluoride, for the production of F-32 in the liquid phase. However, this catalyst is highly corrosive and in fact the use of a special alloy for the reactor is necessary.
The document WO 99/25670 describes the fluorination of F-30 to give F-32 in the liquid phase in the presence of catalysts, such as antimony pentachloride, and in a reactor coated with fluoropolymer, for example (which proves to be essential in view of the corrosive effects which are generated). The document provides for the separation of the products resulting from the reaction in two or three columns, so as to recycle the reactants or coproducts to the reactor and to withdraw a stream of F-32 produced and also a stream of hydrogen chloride, another product of the reaction, in combination with F-32 or separately. This process generates impurities: chlorodifluoromethane (F-22) and trifluoromethane (F-23).
The document WO 01/81353 describes ionic liquids based on titanium, niobium, tantalum, tin or antimony which make it possible to carry out catalytic fluorination in the liquid phase. The fluorination reactions cited include that of F-30 to give F-32.
There is also the need to develop a novel process for the production of difluoromethane which exhibits an improved yield and an improved selectivity, while avoiding bringing about excessive corrosion.